Cytherois gajinensis, Yoo & Thi & Karanovic, 2020

Yoo, Hyunsu, Thi, Van Anh Le & Karanovic, Ivana, 2020, Two Paradoxostomatidae (Ostracoda) species from South Korea with a key to genera of the family, ZooKeys 943, pp. 21-39 : 21

Cytherois gajinensis sp. nov. Figures 1 , 2 , 3

Material examined.

Holotype, male, dissected on one slide (NIBRIV0000813439) and shell on micropalaeontological slide; allotype, female, dissected on one slide and shell on micropalaeontological slide; paratypes: two males dissected on each slides and shell on micropalaeontological slides, one female dissected on one slide and shell on micropalaeontological slide and five specimens kept in a 2 ml vial.

Type locality. South Korea, Gangwon-do, Goseong-gun, Jugwang-myeon, Gajin-ri; 38°18.16'N, 128°34.36'E, 25 m, sandy bottom; 29 Aug. 2016, collected by Raehyuk Jeong and Wonchoel Lee.

Etymology. The species is named after the beach from where it was collected.

Description of male.

Carapace (Figs 1A-C, E-G , 2A ). Relatively small, with L approximately 422 µm, H approximately 154 µm. LV overlapping RV. Carapace elongated ellipsoidal in lateral view (Fig. 1A ). Dorsal margin slightly arched, antero-dorsal and postero-dorsal margins evenly curved, ventral margin slightly sinusoid around mouth region. Anterior and posterior margins rounded, with anterior margin being slightly narrower than posterior one. Greatest H situated slightly behind the middle. Eye present. Surface of the carapace smooth with few simple type setae distributed (Fig. 1E, F ). Marginal pore canals noticeable along ventral and posterior margins (Fig. 2A ), relatively short and not branched. Inner lamella equally wide anteriorly and posteriorly. Muscular scar imprints consisting of a row of four vertical scars and one frontal scar present (Figs 1G , 2A ). Hinge adont (Fig. 1C ).

A1 (Fig. 2C ). Six-segmented. First segment without setulae and setae. Second segment with setule along anterior to distal margin. Third segment with visible setulae along anterior to distal margin and one bare seta on antero-distal margin, not reaching end of fourth segment. Fourth segment with two bare setae on antero-distally, one reaching end of fifth segment and another twice longer than the fifth segment. Fifth segment with two bare setae on antero-distal part, one 1.5 times longer than terminal segment and the other twice as long as terminal segment. Terminal segment with three long bare setae on distal margin, almost 2.5 times longer than terminal segment. L ratio between six segments 4.1: 5.6: 1.7: 1.7: 1.36: 1.

A2 (Fig. 2B ). Five-segmented. Exopod transformed into three-segmented spinneret seta. First endopodal segment without setulae and seta. Second segment with two setae postero-distally: one plumose, seta reaching end of third segment, another bare, reaching 1/3 the third segment. Third segment with setule along posterior to distal margin, and one short, strong, bare seta postero-distally reaching distal end of terminal segment. Penultimate segment with seta transformed into sucking organ. Terminal segment very short and carrying only one strong claw on distal margin. L ratio between five distal segments: 6: 3.1: 4.3: 1: 1.

Md (Fig. 2E ). Coxa with six tiny teeth and three thin, bare, setae on distal margin. Exopod with one seta; endopod 2-segmented. First endopodal segment elongated but not carrying any seta. Second segment with nine setae, five of which arise from central margin, four from distal margin. First segment almost four times longer than second segment.

Mxl (Fig. 2D ). Palp 1-segmented carrying four bare setae on distal margin, all setae almost half as long as the palp. Two long mop-shaped setae ("aberrant setae") present at the distal end of vibratory plate. Masticatory process with three endites, first and second endites each with three bare setae, third endite with four bare setae on distal margin.

L5 (Fig. 3A ). Four-segmented. First segment with two bare setae, one on antero-medial margin, not reaching end of first segment, and another on antero-distally, reaching 1/3 of second segment. Second segment with one bare seta antero-distally, not reaching end of third segment. Penultimate segment without any seta. Terminal segment with one claw like seta on distal margin. Last three segments with setulae along posterior to distal margin. L ratio between four segments 2.7: 1.24: 1: 1.06.

L6 (Fig. 3B ). Four-segmented. First segment with one bare seta antero-distally, reaching 1/4 of second segment. Second segment with one bare seta antero-distally, reaching half of third segment. Following segment without any setae. Terminal segment with one claw like seta on distal margin. Last three segments with setulae along posterior to distal margin. L ratio between four segments 2.2: 1.4: 1: 1.3. In comparison to L5, L6 has more elongated segments.

L7 (Fig. 3C ). Four-segmented. First segment with tiny setule postero-proximally and, antero-medially, and one bare seta on antero-distal margin, reaching 1/4 of second segment. Second segment with one plumose seta on antero-distal margin reaching almost half length of the third segment. Third segment with long, almost spine-like setulae along anterior to distal margin. Terminal segment with one strong claw and one bare seta on distal margin, almost half as long as same segment. Second and terminal segment with setulae along posterior to distal margin. L ratio between four segments 2.9: 2.5: 1: 1.25. Segments of L7 are more elongated than on L5, but less than on L6.

Hp (Fig. 3D ). Basal plate ovate. Distally Hp carrying a large lobe in a shape of eagle beak, dorsally to which a much smaller lobe-like process with triangular, but dull tip present.

Description of female.

Carapace (Fig. 1D ). Slightly larger than males. L approximately 451 µm, H approximately 182 µm. Shape and all other morphological features similar to male.

A2 (Fig. 2B' ). Penultimate segment with one seta instead of sucking organ, and same segment longer than in male. L ratio between five distal segments of female A2. 9: 5.7: 6.5: 3.5: 1.

GF (Fig. 2F ). Basal part rectangular. Two caudal rami present and long setulae cover the surface. End of the body seta not observed.

All other appendages same as in male.

Figures

Figure 1. SEM photographs of Cytherois gajinensis sp. nov. A-C, E-G male D female: A LV external view (holotype) B RV, external view (paratype) C LV, internal view (paratype) D RV, external view (allotype) E, F surface pores (holotype) G muscular scar print (paratype).

Figure 2. Cytherois gajinensis sp. nov. A-E male (holotype) F female (allotype): A RV internal view B A 2 C A 1 D Mxl E Md F, B' GF. All scale bars: 50 µm.

Figure 3. Cytherois gajinensis sp. nov. male (holotype) A L 5 B L 6 C L 7 D Hp. All scale bars: 50 µm.